Previous Issue

Table of Contents

Galaxies, Volume 6, Issue 4 (December 2018)

  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Readerexternal link to open them.
View options order results:
result details:
Displaying articles 1-10
Export citation of selected articles as:
Open AccessArticle The Laboratory Astrophysics Spectroscopy Programme at Imperial College London
Galaxies 2018, 6(4), 109; https://doi.org/10.3390/galaxies6040109
Received: 2 August 2018 / Revised: 2 October 2018 / Accepted: 9 October 2018 / Published: 13 October 2018
PDF Full-text (2743 KB) | HTML Full-text | XML Full-text
Abstract
Accurate atomic parameters, such as transition probabilities, wavelengths, and energy levels, are indispensable for the analysis of stellar spectra and the obtainment of chemical abundances. However, the quantity and quality of the existing data in many cases lie far from the current needs
[...] Read more.
Accurate atomic parameters, such as transition probabilities, wavelengths, and energy levels, are indispensable for the analysis of stellar spectra and the obtainment of chemical abundances. However, the quantity and quality of the existing data in many cases lie far from the current needs of astronomers, creating an acute need for laboratory measurements of matching accuracy and completeness to exploit the full potential of the very expensively acquired astrophysical spectra. The Fourier Transform Spectrometer at Imperial College London works in the vacuum ultraviolet-visible region with a resolution of 2,000,000 at 200 nm. We can acquire calibrated spectra of neutral, singly, and doubly ionized species. We collaborate with the National Institute of Standards and Technology (NIST) and the University of Lund to extend our measurements into the infrared region. The aim of this review is to explain the current capabilities of our experiment in an understandable way to bring the astronomy community closer to the field of laboratory astrophysics and encourage further dialogue between our laboratory and all those astronomers who need accurate atomic data. This exchange of ideas will help us to focus our efforts on the most urgently needed data. Full article
(This article belongs to the Special Issue Atomic and Molecular Data Needs for Astronomy and Astrophysics)
Figures

Figure 1

Open AccessArticle Infrared Observations of the Asymmetric Mass Loss of an AGB Star
Galaxies 2018, 6(4), 108; https://doi.org/10.3390/galaxies6040108
Received: 31 July 2018 / Revised: 9 October 2018 / Accepted: 9 October 2018 / Published: 12 October 2018
PDF Full-text (294 KB) | HTML Full-text | XML Full-text
Abstract
We report on the observations of the circumstellar envelope of the AGB star II Lup in the near- and mid-infrared with the use of direct imaging and interferometric techniques. Our findings indicate that the circumstellar envelope is not spherically symmetric and that the
[...] Read more.
We report on the observations of the circumstellar envelope of the AGB star II Lup in the near- and mid-infrared with the use of direct imaging and interferometric techniques. Our findings indicate that the circumstellar envelope is not spherically symmetric and that the majority of the emission originates within 0.5 arcsec from the star. Full article
(This article belongs to the Special Issue Asymmetric Planetary Nebulae VII)
Figures

Figure 1

Open AccessArticle Testing the Anomalous Growth of the Black Hole Radius from AGN
Galaxies 2018, 6(4), 107; https://doi.org/10.3390/galaxies6040107
Received: 18 July 2018 / Revised: 17 September 2018 / Accepted: 20 September 2018 / Published: 3 October 2018
PDF Full-text (417 KB)
Abstract
We analyze constraints on the anomalous growth of the black hole radius or the black hole spin from the X-rays spectrum data of Active Galactic Nuclei (AGN) in NGC 5506. The anomalous growth of the mass or of the spin of a black
[...] Read more.
We analyze constraints on the anomalous growth of the black hole radius or the black hole spin from the X-rays spectrum data of Active Galactic Nuclei (AGN) in NGC 5506. The anomalous growth of the mass or of the spin of a black hole may be unveiled within the framework of models of alternative gravity, including f ( R ) -gravity. Our phenomenological analysis is based on an effective parametrization for the black hole Kerr metric, which is inspired by the antievaporating solutions discovered by Nojiri and Odintsov. We find tight constraints on the parameter space of anomalous metrics. Intriguingly, we find that a more than secularly growing solution can better fit current data. Our result opens a pathway towards a new phenomenological approach for testing predictions of general relativity and alternative theories of gravity. Full article
Open AccessArticle Investigation of Similarity in the Spectra between Short- and Long-Duration Gamma-ray Bursts
Galaxies 2018, 6(4), 106; https://doi.org/10.3390/galaxies6040106
Received: 8 August 2018 / Revised: 25 September 2018 / Accepted: 26 September 2018 / Published: 3 October 2018
PDF Full-text (458 KB)
Abstract
We investigated the spectral properties of the prompt emission for short- and long-duration gamma-ray bursts (GRBs) using the Fermi Gamma-ray Burst Monitor data. In particular, we focused on comparing the spectral properties of short GRBs and the initial 2 s of long GRBs,
[...] Read more.
We investigated the spectral properties of the prompt emission for short- and long-duration gamma-ray bursts (GRBs) using the Fermi Gamma-ray Burst Monitor data. In particular, we focused on comparing the spectral properties of short GRBs and the initial 2 s of long GRBs, motivated by the previous study of Ghirlanda et al. (2009). We confirmed the similarity in the low energy photon index α between short GRBs and the initial 2 s of long GRBs. Since about a quarter of our spectra of both short GRBs and the initial 2 s of long GRBs show α to be shallower than - 2 / 3 , it is difficult to understand in the context standard synchrotron emission. Full article
Open AccessArticle The VAMDC Portal as a Major Enabler of Atomic and Molecular Data Citation
Galaxies 2018, 6(4), 105; https://doi.org/10.3390/galaxies6040105
Received: 25 June 2018 / Revised: 20 September 2018 / Accepted: 25 September 2018 / Published: 3 October 2018
PDF Full-text (2045 KB)
Abstract
VAMDC bridged the gap between atomic and molecular (A&M) producers and users through providing an interoperable e-infrastructure connecting A&M databases, as well as tools to extract and manipulate those data. The current paper highlights the usage of the VAMDC Portal, recalls how data
[...] Read more.
VAMDC bridged the gap between atomic and molecular (A&M) producers and users through providing an interoperable e-infrastructure connecting A&M databases, as well as tools to extract and manipulate those data. The current paper highlights the usage of the VAMDC Portal, recalls how data citation is implemented within VAMDC and provides insights about usage of VAMDC that will increase the impact factor of A&M producers and will offer a more reliable citation of A&M datasets included in application fields. Full article
(This article belongs to the Special Issue Atomic and Molecular Data Needs for Astronomy and Astrophysics)
Open AccessArticle Towards Exascale Simulations of the ICM Dynamo with WENO-Wombat
Galaxies 2018, 6(4), 104; https://doi.org/10.3390/galaxies6040104
Received: 28 August 2018 / Revised: 25 September 2018 / Accepted: 27 September 2018 / Published: 29 September 2018
PDF Full-text (826 KB) | HTML Full-text | XML Full-text
Abstract
In galaxy clusters, modern radio interferometers observe non-thermal radio sources with unprecedented spatial and spectral resolution. For the first time, the new data allows to infer the structure of the intra-cluster magnetic fields on small scales via Faraday tomography. This leap forward demands
[...] Read more.
In galaxy clusters, modern radio interferometers observe non-thermal radio sources with unprecedented spatial and spectral resolution. For the first time, the new data allows to infer the structure of the intra-cluster magnetic fields on small scales via Faraday tomography. This leap forward demands new numerical models for the amplification of magnetic fields in cosmic structure formation—the cosmological magnetic dynamo. Here we present a novel numerical approach to astrophyiscal MHD simulations aimed to resolve this small-scale dynamo in future cosmological simulations. As a first step, we implement a fifth order WENO scheme in the new code WOMBAT. We show that this scheme doubles the effective resolution of the simulation and is thus less expensive than common second order schemes. WOMBAT uses a novel approach to parallelization and load balancing developed in collaboration with performance engineers at Cray Inc. This will allow us scale simulation to the exaflop regime and achieve kpc resolution in future cosmological simulations of galaxy clusters. Here we demonstrate the excellent scaling properties of the code and argue that resolved simulations of the cosmological small scale dynamo within the whole virial radius are possible in the next years. Full article
(This article belongs to the Special Issue The Power of Faraday Tomography)
Figures

Figure 1

Open AccessArticle Reverse Shock Emission from Short GRBs
Galaxies 2018, 6(4), 103; https://doi.org/10.3390/galaxies6040103
Received: 14 August 2018 / Revised: 20 September 2018 / Accepted: 25 September 2018 / Published: 28 September 2018
PDF Full-text (4295 KB) | HTML Full-text | XML Full-text
Abstract
We investigate the expected radio emission from the reverse shock of short GRBs, using the fitted afterglow parameters. In light of recent results suggesting that in some cases the radio afterglow is due to emission from the reverse shock, we examine the extent
[...] Read more.
We investigate the expected radio emission from the reverse shock of short GRBs, using the fitted afterglow parameters. In light of recent results suggesting that in some cases the radio afterglow is due to emission from the reverse shock, we examine the extent to which this component is detectable for short GRBs. In some GRBs, the standard synchrotron shock model predicts detectable radio emission from the reverse shock when none was seen. Many physical parameters play a role in these estimates, and our results highlight the need to explore the fundamental processes involved in GRB particle acceleration and emission more deeply. However, with a more rapid follow-up, we can test our standard model of GRBs, which predicts an early, radio bright reverse shock in many cases. Full article
Figures

Figure 1

Open AccessArticle Binary Interactions, High-Speed Outflows and Dusty Disks during the AGB-To-PN Transition
Galaxies 2018, 6(4), 102; https://doi.org/10.3390/galaxies6040102
Received: 9 July 2018 / Revised: 12 September 2018 / Accepted: 13 September 2018 / Published: 25 September 2018
PDF Full-text (324 KB) | HTML Full-text | XML Full-text
Abstract
It is widely believed that the dramatic transformation of the spherical outflows of AGB stars into the extreme aspherical geometries seen during the planetary nebula (PN) phase is linked to binarity and driven by the associated production of fast jets and central disks/torii.
[...] Read more.
It is widely believed that the dramatic transformation of the spherical outflows of AGB stars into the extreme aspherical geometries seen during the planetary nebula (PN) phase is linked to binarity and driven by the associated production of fast jets and central disks/torii. The key to understanding the engines that produce these jets and the jet-shaping mechanisms lies in the study of objects in transition between the AGB and PN phases. I discuss the results of our recent studies with high-angular-resolution (with ALMA and HST) and at high-energies (with GALEX, XMM-Newton and Chandra) of several such objects, which reveal new details of close binary interactions and high-speed outflows. These include two PPNe (the Boomerang Nebula and IRAS 16342-3814), and the late carbon star, V Hya. The Boomerang Nebula is notable for a massive, high-speed outflow that has cooled below the microwave background temperature, making it the coldest object in the Universe. IRAS 16342-3814 is the prime example of the class of water-fountain pre-planetary nebulae or PPNe (very young PPNe with high-velocity H2O masers) and shows the signature of a precessing jet. V Hya ejects high-speed bullets every 8.5 years associated with the periastron passage of a companion in an eccentric orbit. I discuss our work on AGB stars with strongly-variable high-energy (FUV, X-ray) emission, suggesting that these objects are in the early stages of binary interactions that result in the formation of accretion disks and jets. Full article
(This article belongs to the Special Issue Asymmetric Planetary Nebulae VII)
Figures

Figure 1

Open AccessArticle The Formation of Fullerenes in Planetary Nebulae
Galaxies 2018, 6(4), 101; https://doi.org/10.3390/galaxies6040101
Received: 31 July 2018 / Revised: 18 September 2018 / Accepted: 18 September 2018 / Published: 21 September 2018
PDF Full-text (337 KB) | HTML Full-text | XML Full-text
Abstract
In the last decade, fullerenes have been detected in a variety of astrophysical environments, with the majority being found in planetary nebulae. Laboratory experiments have provided us with insights into the conditions and pathways that can lead to fullerene formation, but it is
[...] Read more.
In the last decade, fullerenes have been detected in a variety of astrophysical environments, with the majority being found in planetary nebulae. Laboratory experiments have provided us with insights into the conditions and pathways that can lead to fullerene formation, but it is not clear precisely what led to the formation of astrophysical fullerenes in planetary nebulae. We review some of the available evidence, and propose a mechanism where fullerene formation in planetary nebulae is the result of a two-step process where carbonaceous dust is first formed under unusual conditions; then, the fullerenes form when this dust is being destroyed. Full article
(This article belongs to the Special Issue Asymmetric Planetary Nebulae VII)
Figures

Figure 1

Open AccessConference Report Challenges and Techniques for Simulating Line Emission
Galaxies 2018, 6(4), 100; https://doi.org/10.3390/galaxies6040100
Received: 3 July 2018 / Revised: 24 August 2018 / Accepted: 1 September 2018 / Published: 20 September 2018
PDF Full-text (2665 KB) | HTML Full-text | XML Full-text
Abstract
Modeling emission lines from the millimeter to the UV and producing synthetic spectra is crucial for a good understanding of observations, yet it is an art filled with hazards. This is the proceedings of “Walking the Line”, a 3-day conference held in 2018
[...] Read more.
Modeling emission lines from the millimeter to the UV and producing synthetic spectra is crucial for a good understanding of observations, yet it is an art filled with hazards. This is the proceedings of “Walking the Line”, a 3-day conference held in 2018 that brought together scientists working on different aspects of emission line simulations, in order to share knowledge and discuss the methodology. Emission lines across the spectrum from the millimeter to the UV were discussed, with most of the focus on the interstellar medium, but also some topics on the circumgalactic medium. The most important quality of a useful model is a good synergy with observations and experiments. Challenges in simulating line emission are identified, some of which are already being worked upon, and others that must be addressed in the future for models to agree with observations. Recent advances in several areas aiming at achieving that synergy are summarized here, from micro-physical to galactic and circum-galactic scale. Full article
Figures

Figure 1

Back to Top